It is known to apply a control voltage to the input, generally designated by RESET, of a microprocessor for reinitializing this latter at the time of mains power supply cuts. It is also known, in the case where the execution of a safeguard subprogram is required, to apply this control voltage at a time delayed with respect to a time of detection of the disappearance of the mains by a sufficiently long period to allow a program to be executed for safeguarding the instruction which is being executed.
This arrangement however has the disadvantage that it does not give any guarantee as to the operation of the microprocessor when the output voltage of the power supply disappears for a cause other than that of the disappearance of the mains voltage, such an event possibly occurring in the case, more especially, of a short circuit across the power supply output or else in the case of accidental disconnection of the card holder of the microprocessor from its power supply. In these cases, in fact, the voltage for reinitializing the microprocessor cannot be applied to the RESET input because the mains voltage is still present and the supply voltage of the microprocessor disappears. This causes uncertain operation of the microprocessor which may generate, on its input-output channel, erratic data which may adversely affect the operation of reception devices coupled to the microprocessor over this channel.
In the case where the execution of a safeguard sub program is not required, the known arrangement has the additional disadvantage of pointlessly complicating the power supply of the microprocessor, for it does not seem indispensable in this case to have a logic signal prior to the beginning of the decrease of the power supply voltage of the microprocessor when it would be sufficient simply to apply to the RESET input a logic voltage equal to 0 volt as soon as the power supply voltage of the microprocessor disappears.